This invention relates to electronic power supplies, and more particularly to small light-weight switching regulator supplies for relatively low power requirements.
Most of the present day electronic systems are comprised of assemblies of various integrated circuits requiring but very moderate amounts of well-regulated electrical power. A total system of integrated circuit subassemblies may require only one or two amperes of a low level regulated voltage and it has been estimated that ninety percent of all electronic subsystems that include a power supply require less than 30 watts of regulated D.C. power.
Until quite recently, nearly all commercially available commercial power supplies operated by transforming and rectifying the A.C. power to a voltage somewhat higher than the desired regulated voltage and then by a process that required the dissipation of substantial amounts of power, provide the necessary regulation to assure constant output voltage levels regardless of variations in the load or the input line voltage. While such regulated power supplies operated quite effectively, they were very inefficient and the power dissipation produced substantial amounts of heat requiring the extensive use of heat sinks and other cooling devices to avoid the excessively high operating temperatures that would seriously degrade the reliability of the power supply.
Recently, power supply development is being concentrated toward the high efficiency switching regulators which dissipate a minimum of electrical power and therefore obviate the need for complex cooling schemes and devices. Switching regulators are generally voltage regulating circuits which sample the regulator output voltage, compare it with a voltage reference, and use the error voltage to control an electronic switch in line between the unregulated D.C. source and filtering circuitry which smooths out the interruptions caused by the switching action into a constant D.C. voltage at a level determined by the reference voltage level. In order to properly regulate between no-load and a maximum load, it is apparent that the in-line electronic switch continually oscillates to produce a minimum of ON-time at no-load to a maximum of ON-time at maximum load. Because this random switching greatly complicates the circuit design, nearly all switching regulators now drive the in-line switches with circuits containing oscillators that either operate at a fixed frequency and vary the pulse width or, alternately, provide constant pulse widths and vary the pulse frequency for applying the unregulated D.C. voltage to the filter circuitry.